Such processes for producing a composite web have been known. For example, European Patent Specification No. EP-PS 0,109,924 discloses a process in which a substrate web is coated on both sides with an adhesive. The substrate web thus coated is then sent via one of the two applicator rollers, which together form a first roller gap, to a second roller gap, which is formed by an applicator roller and a first laminating roller. In the second roller gap, the substrate web is bonded to a laminating web fed in via the first laminating roller. The two webs bonded together are subsequently passed over the first laminating roller in a third roller gap which is formed by a second laminating roller and a first laminating roller. Via the second laminating roller, a second laminating web is fed in, and is bonded in the third roller gap to the other two webs already bonded together to form a triple composite web.
Using this process, it is possible to use many types of composite webs with different materials of the substrate web and the laminating web, as well as adhesives that are adapted to these materials, of which the different webs consist. The thicknesses of the webs may also be different. The adhesive layer thicknesses can be adjusted to the actual needs.
Since no rolling behavior may occur in the finished composite web, it is necessary to control the tensions of all webs. This web tension control depends to a great extent on the temperatures affecting the web, at which the adhesives must be processed.
A defined adhesive, which must be processed at its characteristic temperature and at a viscosity that depends on this temperature, is required whenever two webs, which consist of different materials and may have greatly different thicknesses, are to be joined. The above-described process does not make it possible to join a substrate web on both sides with a laminating web, which webs consist of different materials and for which adhesives with greatly different processing temperatures must be used. Until the adhesive- coated substrate web is joined with the laminating webs, the two have adapted themselves to different adhesive temperatures, so that optimal temperatures and consequently optimal viscosities will no longer prevail at the connection site to the laminating web. This may affect the quality of the junction.
This process also fails to provide for application of an adhesive layer to the web which would be best suited by virtue of the material properties and the surface structure. The adhesive is always applied to the substrate web, and this can also affect the amount of adhesive applied.